1. Field of the Invention
The present invention relates to water tanks, and specifically to an automatic flushing system for flushing accumulated sediment from electric and gas hot water tanks and the like.
2. Description of the Prior Art
Hot water tanks provide a well known means for providing a source of domestic and commercial hot water. Conventional hot water tanks include a cylindrical glass lined water holding tank structure enclosed within a metal tank cover. An electric hot water tank uses electric heating elements projecting into the water holding tank to raise and maintain the water temperature. Typically, a plurality of electric heating elements are arranged in spaced vertical configuration. Similarly, gas hot water tanks include one or more heat exchangers in thermal contact with the water within the tank.
Such tanks further include various piping connections including cold water feed piping which supplies water to the tank, hot water feed piping for delivering hot water to various plumbing fixtures and a valved drain typically located on the sidewall of the tank, near the bottom. Since water tends to stratify along various temperature gradients, the hot water within the tank migrates toward the top, while colder water within the tank migrates toward the bottom. Accordingly, the hot water feed piping draws water from the top of the tank, while the cold water feed piping extends downward via a cold water fill tube, terminating near the bottom of the tank, for introducing cold water at the bottom of the tank.
A common problem experienced with all hot water tanks involves the accumulation of sediment at the bottom of the tank. This problem results from the precipitation of sediment out of the water in the tank, which sediment settles to the bottom of the tank. While the composition of the sediment, and the degree of accumulation naturally depends on the quality of the water supply, the problem persists and the accumulation of sediment greatly reduces the efficiency and operating life of the tank. For example, accumulated sediment is a thermal insulator and the accumulation of sediment on the heating elements reduces heat transfer efficiency. In electric hot water tanks, sediment can accumulate to the point where one or more of the lower electric heating elements are completely covered, thereby drastically reducing heat transfer efficiency and causing premature failure of the heating element(s) by overheating and burnout. Furthermore, the accumulation of sediment in the tank contributes to accelerated corrosion, ultimately leading to leaks which require the wholesale replacement of the tank.
Accordingly, several prior art patents are directed to solving the problems associated with sediment accumulation. For example, U.S. Pat. No. 4,714,053, issued to Perry, discloses a water heater cleaning apparatus which includes a water supply tube terminating in a nozzle for forming a horizontal spray pattern along the tank bottom for flushing sediment toward the tank drain. However, conventional hot water tanks do not include the additional piping and nozzle arrangement required by the Perry device.
U.S. Pat. No. 5,152,843, issued to McDonald et al. discloses a method for removal of hot water heater sediment which involves shutting off and draining the tank, and the insertion of a water-jet probe to direct a water jet toward accumulated sediment.
U.S. Pat. No. 4,790,289, issued to Barrett, discloses a sediment agitating apparatus for a water heater to aid in preventing sediment buildup. The agitating mechanism includes a pump for drawing water from the top of the tank and discharging the water at the bottom of the tank. As discussed above, however, mixing hot water from the top of the tank with cold water from the bottom of the tank is undesirable.